Traefik is an open source HTTP reverse proxy and load balancer. From 3.6.11 until 3.6.25 and 3.7.10, Traefik's BasicAuth middleware in pkg/middlewares/auth/basic_auth.go deduplicates concurrent password checks with a singleflight key built from the delimiter-free concatenation of password and secret, allowing an attacker who has a valid credential and the stored hash to authenticate as an unconfigured username when headerField trusts the forwarded identity. This issue is fixed in 3.6.25 and 3.7.10.
Affected: Go: github.com/traefik/traefik/v3
## Summary
There is a low severity vulnerability in Traefik's BasicAuth middleware. Concurrent password verifications are deduplicated through a singleflight group whose key was the delimiter-free concatenation of the submitted password and the stored secret, so a request carrying an unconfigured username β whose secret is empty β can produce the same key as a configured user's valid request and receive that request's successful result. Exploitation requires the attacker to already hold a valid credential **and** to read the stored password hash, which is only reachable through paths that are themselves privileged: the API is documented as admin-only, the Kubernetes path requires read access to the Secret, and the Docker path requires access to the socket. The key now encodes the password length as a prefix, so distinct (password, secret) pairs can no longer collide. Only the v3.6 line from v3.6.11 onwards and the v3.7 line are affected; earlier v3 releases and the v2 line do not carry the vulnerable deduplication path.
## Patches
- https://github.com/traefik/traefik/releases/tag/v3.6.25 - https://github.com/traefik/traefik/releases/tag/v3.7.10
## For more information
If you have any questions or comments about this advisory, please [open an issue](https://github.com/traefik/traefik/issues).
<details> <summary>Original Description</summary>
## Summary
Traefik's BasicAuth middleware deduplicates concurrent password checks with a `singleflight.Group`. Its key is the deβ¦